bgc code coverage

[eclare108213]

@njeffery Please let us know the proper namelist combinations to exercise these portions of the bgc code. The runs don't have to be science-worthy, we just need to be able to test the code to make sure changes are BFB, no segfaults, divzero, etc. Thanks!

What else needs to be on/off or otherwise set to run these:
skl_bgc = T
dEdd_algae = T
model_aero = T
solve_zsal = T

turn on DIC, Chl, Fe

It would be great to have a minimal, optimal-in-terms-of-coverage, yet somewhat realistic bgc test suite.

Also, get_forcing_bgc.F90 looks like it has a bug in it -- we're using the ISPOL and NICE datasets, but it doesn't look like the code to read them is exercised. ??? Maybe we don't have the namelist combos correct for these tests either.

[eclare108213]

Skeletal layer tests (skl_bgc) were added in PR #199. Still to do:

1. Limit time span of NICE tests to the dates when the forcing data is valid, and don't test restarts.
2. Add skl tests to the standard suite.
3. Check remaining code coverage items above.
4. Add namelist fields for forcing filenames rather than having them hardwired in the code.

[eclare108213]

PR #203 addresses items 1 and 2 above.

[eclare108213]

PR #203 now also addresses item 4.

[eclare108213]

The remaining item is code coverage, which is covered in #194